To find Mr. Wong's first-month bonus, we work backwards from the given expenditures and remaining amount. After calculating the expenses for the ring and the mangoes and knowing he has $100 left, we find that his bonus was $400.
To determine Mr. Wong's first-month bonus, we need to work backwards from the information given. Let's denote his bonus as B.
So, Mr. Wong's first-month bonus was $400.